JPH02289441A - Production of optical fiber - Google Patents

Abstract

PURPOSE:To produce a good optical fiber from a preform with the fiber parameter deviated from the set value to some extent by controlling the drawing tension so that the cutoff wavelength of the drawn single-mode fiber conforms to that of the produced fiber. CONSTITUTION:The vitrified preform 1 is set in a preform delivery device 3 and arranged in a heating furnace 4 to heat and melt the tip of the preform 1, and a fiber 2 is drawn out from the tip. The drawing tension of the fiber 2 is measured by a tension monitor 9, and the winding force of a winding roller 10 is adjusted so that the measured value for the drawing tension is held at a specified value. The drawing tension for the cutoff wavelength of the fiber 2 to conform to the allowable value for the cutoff wavelength in the single-mode fiber to be produced is derived from the relational curve between the predetermined drawing tension and the cutoff wavelength of the obtained fiber 2, and the drawing tension is adjusted to the specified value.

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention relates to a method of manufacturing a single mode fiber used as an optical fiber for communication, etc. Regarding how to do it even at this stage.

"Prior Art and its Problems" Single-mode fibers, graded fibers, and the like are generally known as optical fibers used for communications. These optical fibers are used with different characteristics depending on the application, and when manufacturing the optical fibers, it is necessary to optimally design and control the refractive index distribution of the core.

Traditionally, to manufacture these optical fibers, VAD
A porous base material is produced by a method such as a method or an OVD method, and then the porous base material is dehydrated and sintered to produce a transparent glass base material,
Next, the transparent glass base material is drawn to produce a fiber.

At this time, the characteristics of the fiber (mode field diameter, cutoff wavelength, dispersion characteristics) are mainly determined by the refractive index distribution at the time of manufacturing the base material, and the refractive index distribution is maintained even after being drawn into a fiber. It is believed that.

The refractive index distribution of the base material is adjusted using the VAD method and OV method.
In method D, this is done at the time of deposition and dehydration and sintering, and no consideration has been given to adjusting the properties of the fiber in the process after it is made into a transparent glass base material.

Here, to explain base material manufacturing by VAD method as an example, first, 810. A porous base material is prepared by depositing . The core has @amount of Doban) (G eO,,
P! 05, etc.) to obtain a predetermined refractive index distribution by temperature control. This porous matrix is then dehydrated and sintered. At this stage, only a portion of the core and cladding of the optical fiber have been manufactured in the sintered body, so dimensions are further adjusted using the external method and jacket method. (hereinafter referred to as a preform) is produced. At this time, if there are mechanical troubles or fluctuations in the exhaust suction pressure, the cladding thickness may vary, and as a result, predetermined fiber parameters may not be obtained.

In such a case, it is possible to take measures such as polishing the preform or reattaching it to the outside, but all of these operations are extremely inefficient.

Further, in some cases, the refractive index distribution of the core is limited, and the above adjustment by adjusting the cladding thickness may not be able to improve the problem.

As described above, preforms for which predetermined parameters cannot be obtained cannot be used as preforms for manufacturing fibers, and there is a problem in that the yield when manufacturing preforms is low.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a manufacturing method that can manufacture a good quality single mode fiber from a preform whose fiber parameters slightly deviate from the set values when manufacturing a single mode fiber. The purpose is

"Means for Solving the Problems" The present invention provides a method for manufacturing a single mode fiber by drawing a transparent preform for optical fiber, in which the cutoff wavelength of the drawn single mode fiber is the same as that of the single mode fiber to be manufactured. The solution to the above problem is to draw the wire by controlling the drawing tension for each preform so as to match the cutoff wavelength of the preform.

1 Effect" By varying the drawing tension during drawing of the preform, the cutoff wavelength of the single mode fiber to be produced changes at a substantially constant rate. Parameters other than the cutoff wavelength also vary depending on the drawing tension, but the amount of variation in other parameters is small compared to the amount of variation in the cutoff wavelength. By keeping the parameters within the permissible values of the fiber, other parameters are less likely to deviate from their respective permissible values.

Hereinafter, the method of the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a diagram showing an example of a drawing apparatus suitable for carrying out the method of the present invention, in which reference numeral 1 represents a preform and 2 represents a fiber.

This preform 1 is produced by dehydrating and sintering a porous base material produced by a method such as a VAD method or an OVD method to make it transparent vitrified.

Normally, the refractive index distribution of the sintered base material is analyzed in its bulk state using an analysis device such as a preform analyzer, and the fiber characteristics are estimated from the refractive index distribution. The estimated value is then used to determine the quality of the base material and provide feedback to the previous process. In the present invention, it is possible to use not only good products whose cutoff wavelength of the preform l matches the tolerance values of preforms for manufacturing single mode fibers, but also defective products whose parameters slightly deviate from the tolerance values. .

To draw the preform 1, the prepared preform 1 is placed in the preform delivery device 3, and the preform 1 is placed in the heating furnace 4 to heat and melt the tip of the preform 1. Then, the fiber 2 is pulled out from the tip of the preform l, and this fiber 2
Coating cup 5.6 for primary coating and crosslinking tube 7,
The optical fiber 1 is passed through a UV lamp 8 or a UV lamp, and then passed through a tension monitor part 9, and then wound onto a take-up roller 10 to form the optical fiber 1 with a coating applied to the single mode fiber bare wire.
1 is produced.

Note that the outer diameter of the drawn fiber 2 is measured by an outer diameter measurement 512 provided between the heating furnace 4 and the coating cup 5, and the outer diameter of the coated optical fiber 1
The outer diameter of the tube 1 is measured by an outer diameter measuring device 13 provided between the bridge tube 8 and the tension monitor part 9.

The drawing tension of the fiber 2 during this drawing is measured by a tension monitor part 9, and the drawing tension is adjusted by adjusting the winding force of the winding roller 10 so that the measured value of the drawing tension becomes a predetermined value. Make adjustments. This drawing tension is calculated from the relationship curve between the drawing tension determined in advance and the obtained cutoff wavelength of fiber 2, so that the cutoff wavelength of fiber 2 falls within the allowable value of the cutoff wavelength of the single mode fiber to be manufactured. A matching drawing tension is derived, and the drawing tension is adjusted to the predetermined drawing tension.

FIG. 2 is a graph showing an example of a relationship curve between the drawing tension and the cutoff wavelength of the fiber, which is used to set the drawing tension. This relationship curve was graphed by drawing the preform 1 using the drawing device shown in Figure 1 and measuring the cutoff wavelength of the fiber produced by varying the drawing tension in the range of 809 to 280 g. It is.

As is clear from FIG. 2, there is a correlation between the cutoff wavelength and the drawing tension, and the value can be adjusted by adjusting the drawing tension.

Further, the adjustable range of the drawing tension is about 80 to 2809, and if it deviates from this range, the fiber strength, fiber diameter, etc. will be affected. This tension adjustment range is very wide in terms of the cutoff wavelength of the obtained fiber, which is 0.45 μm for a general single mode fiber and a 0.16 μm 1 dispersion shifted fiber, which is within the allowable standard for the cutoff wavelength for both normal fibers. This corresponds to the range of .

It is thought that this variation in each fiber parameter due to the variation in drawing tension causes a change in the stress distribution within the fiber, and this change in stress distribution causes a change in the refractive index distribution.

Note that the drawing tension shown in FIG. 2 is the tension of the fiber after being coated as measured by the tension monitor part 9 shown in FIG. 1, and the actual tension applied to the fiber depends on the drawing speed and coating diameter. It depends.

As described above, the method of the present invention utilizes the fact that the cutoff wavelength of the manufactured fiber changes at a substantially constant rate by varying the drawing tension during drawing of the preform. Since the wire is drawn while adjusting the drawing tension so that the cutoff wavelength of the single mode fiber matches the cutoff wavelength tolerance of the single mode fiber to be manufactured, good products can be obtained from preforms whose cutoff wavelength is slightly outside the predetermined range. Fibers can be produced and the yield of preforms can be improved. In addition, even if the cutoff wavelength is within a predetermined range but deviates from the center value, good quality fiber can be manufactured by adjusting the drawing tension and drawing so that the cutoff wavelength of the fiber becomes the center value. can do.

Parameters other than the cut-off wavelength also vary depending on the drawing tension, but the amount of variation in other parameters is small compared to the amount of variation in the cut-off wavelength. By keeping the fiber parameters within the permissible values, other parameters are less likely to deviate from their respective permissible values.

(Example 1) A quartz-based single mode fiber was manufactured using the drawing apparatus shown in FIG.

The estimated cutoff wavelength for the preform is 1.08.
A micrometer was used. Since the standard cut-off wavelength of the single mode fiber to be manufactured is 1.12 μm or more, the preform would normally be a defective product.

Using this preform, the drawing tension was set to the normal value (110
When the cutoff wavelength of the obtained fiber was 1.14 μm, a fiber satisfying the standard was fabricated. Also, the mode field diameter of the fiber has been reduced by about 0.1 μm, but there is no particular problem in terms of the mode field diameter standard12. Note that the cutoff wavelength of a fiber obtained by drawing the same preform at a normal drawing tension is approximately 1.
It was confirmed that the cutoff wavelength of the fiber was improved by increasing the drawing tension.

In addition, the obtained fiber (cutoff wavelength is 1.14 μm
When the temperature characteristics and H2 characteristics of the fiber produced under normal tension were examined, no significant difference was observed between the fiber and the fiber produced under normal tension.

(Example 2) A 1.55 μm dispersion shifted fiber was fabricated using a preform with a small cutoff wavelength of 0.98 μm in terms of estimated characteristics. The preform is placed in the drawing device shown in Figure 1, and the drawing tension is 3
A fiber was produced by drawing the fiber to a height of 0 g.

The resulting fiber had a long cup-off wavelength of 1.10 μm. improved. Also, the mode field diameter is 0
．． It became smaller by 1 μm. Therefore, the bending properties were improved.

"Effects of the Invention" The optical fiber manufacturing method according to the present invention adjusts the drawing tension for each preform so that the cutoff wavelength of the drawn fiber matches the cutoff wavelength tolerance of the single mode fiber to be manufactured. Since the fiber is drawn while performing this, it is possible to produce a good quality fiber using a preform whose cutoff wavelength is slightly outside the predetermined range, and it is possible to avoid improving the yield of preforms.

In addition, even if the cutoff wavelength is within a predetermined range but deviates from the center value, the cutoff wavelength can be improved by adjusting the drawing tension and drawing so that the fiber cutoff wavelength becomes the center value. fibers of good quality can be manufactured.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of a wire drawing apparatus suitably used to carry out the method of the present invention, and FIG. 2 is a graph showing the relationship between wire drawing tension and cutoff wavelength. ! ...Preform 2...Fiber. 1 diagram distributor Fujikura Electric Cable Co., Ltd.

Claims (1)

[Claims] In a method for producing a single mode fiber by drawing a transparent base material for optical fiber, the drawing tension is controlled so that the cutoff wavelength of the drawn single mode fiber matches the cutoff wavelength of the single mode fiber to be produced. 1. A method of manufacturing an optical fiber, the method comprising: drawing the optical fiber.